The concept of attention has within the past decade become the focal point of research and theory in human learning. Attention is represented as a stimulus encoding process, and research on the selectivity and variability of this process has contributed to the development of theories of human learning and memory. A program of research is proposed which will investigate 1) the relationship between encoding processes and the effects of repetition on short-term memory and long-term memory, 2) the nature of task demands which affect the type of encoding a subject uses, and 3) variables which affect the speed of the encoding process or the probability of encoding along particular stimulus dimensions when stimulus duration is brief. The basic method is the probe memory procedure, modified to allow experimental control over encoding processes. This research will contribute to the development of theories of the effects of repetition on memory, and to the understanding of the role of encoding processes in human learning and memory.